Molded swellable packers

ABSTRACT

Embodiments of the present invention provide a swellable packer and a process for manufacturing swellable packers that may be used for sealing off chambers within a well bore. Various embodiments of the present invention include a variety of in situ molding techniques, such as injection molding and compression molding. Furthermore, some embodiments of the present invention include centering end caps about a tube and securing the end caps to the tube. In these embodiments, the swellable packer can then be molded about the tube and the position of the end caps can be used to determine the position of the outer surface of the swellable polymer with respect to the tube.

BACKGROUND OF THE INVENTION

In the oil and natural gas industry, wells are used to extract oil and natural gas from within the earth. A well is typically defined by a bore formed into the earth. Over time, the flow of oil or natural gas being withdrawn from a well can diminish, reducing the production of the well. Therefore, the industry has developed a variety of methods for increasing the oil or natural gas withdrawn from the well.

One such method is hydraulic fracturing, which typically begins with isolating a portion of the well located above the bottom of the well by sealing a section of the bore wall. The seal is generally made by placing one or more plugs along the depth of the bore, wherein the plugs seal against the bore wall. Between two of these plugs, or between a plug and the top or the bottom of the well, a chamber can be defined. These chambers can then be subjected to very high pressures of water or other fluids, causing the walls of the bore to fracture. This process can create additional flow of oil or natural gas into the chamber once the pressure is released.

Generally, the plugs are formed by swellable packers. In order to create a swellable packer, a tube is wrapped with a polymer which swells when exposed to oil and/or water. The swellable packer is designed to have an outer diameter slightly smaller than the bore diameter. Thus, the swellable packer can be placed down the bore in an unswelled state. Oil or water is then brought into contact with the packer, causing it to swell and seal against the wall of the bore. Once the seal is in place against the wall of the bore, the pressurized chambers can be defined for fracturing the bore wall.

A complication in wrapping the swellable polymer about a tube to create the swellable packer is that the tubes may be out-of-round or bent along the axis of the tube. The tube may be out of round by up to 0.045″ or bent along the axis up to 1″ and still be considered to be within the acceptable specification. However, if the outer diameter of the packer is out-of-round or bent by similar amounts, then the ability for the packer to properly seal against the bore wall is degraded. The current technique compensates for the tube being bent or out-of-round by mounting the tube and packer on a lathe after the packer has been formed, and then machining the outer diameter of the packer to make it perfectly round. This, of course, adds an extra step to the process of forming a swellable packer. Thus, it is desirable to find a more efficient way to form these packers.

BRIEF SUMMARY OF THE INVENTION

These and other advantages are provided by the swellable downhole packers and improved processes of manufacturing provided by the present invention. Advantageously, embodiments of the present invention provide a method for manufacturing a swellable packer comprising the steps of: positioning one or more end caps on the support tube, the end caps defining a size and shape; positioning the end caps and support tube on one or more corresponding supports of an open mold cavity; closing the mold cavity; molding swellable polymer in molten form within the mold cavity and around the support tube; and opening the mold cavity. The molding step may be completed using a variety of molding techniques including injection molding, compression molding, or another molding technique.

In other embodiments, a swellable packer is provided wherein the location of the outer surface of the swellable packer in an unswollen state is determined by the position of the end caps on the tube. Additionally, some embodiments provide a swellable packer with steps along the length of the packer or other unique profiles.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a partially sectional view of an oil or gas well showing the position of two swellable packers in a bore;

FIG. 2 is a perspective view of a swellable packer according to embodiments of the present invention;

FIGS. 3A-D are perspective views illustrating some of the steps of the method of manufacturing a swellable packer according to an embodiment of the present invention;

FIGS. 4A-D are cross-sectional views illustrating some of the steps of the method of manufacturing a swellable packer according to various embodiments of the present invention; and

FIG. 5 is an expanded and partially cross-sectional view of one end of a swellable packer according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

FIG. 1 illustrates an oil or natural gas well that defines a bore 12. Positioned in the bore 12 are two swellable packers 10. These swellable packers 10, when fully swollen, create a chamber 18 that can be pressurized between the swellable packers. The swellable packers 10, in the illustrated embodiment, are both supported on a support tube 11. This support tube 11 can be made of a steel tube or any other suitable material. In some embodiments, the support tube 11 could be used for allowing other downhole components to extend down the bore. The support tube 11 may also be completely or partially blocked along its length.

FIG. 2 is a closer view of one of the swellable packers 10. The swellable packer 10 of the illustrated embodiment is comprised of a swellable polymer 13 that is secured to the support tube 11. The swellable packer 10 should define a length along the support tube 11 sufficient to adequately seal the bore, and in one embodiment this length may be 24″. The swellable packer may be provided with end caps 14 at one or both ends of the swellable packer. The end caps 14 can be formed of metal, carbon, or other resilient material and have a chamfered or tapered portion (as best seen in FIG. 5) that helps guide the swellable packer 10 through the bore as the support tube 11 is lowered or raised in the bore.

One particularly advantageous swelling polymer 13 is available from Tendeka under model no. JSSEO-5. This proprietary formulation provides strong swelling and sealing characteristics. However, other swellable polymers from other manufacturers could be used in embodiments of the present invention.

In one embodiment of the present invention, as mentioned above, end caps 14 are fastened to the tube. The inner diameter of the end caps 14 may be slightly larger than the outer diameter of the tube 11. For example, there might be a 0.030″ difference between the inner diameter of the end caps 14 and the outer diameter of the tube 11. In this example, three or four shims of 0.015″ thickness might be used when securing the end cap 14 to the tube 11 to ensure the end caps 14 are centered on the tube 11. The end caps 14 may be held to tube 11 using screws; in one embodiment 8 to 12 screws may be used. In various embodiments it is important to ensure the end caps 14 are centered about the tube, as in these embodiments the position of the end caps 14 may determine the position of the outer surface of the swellable polymer 13 with respect to the tube 11, as discussed below.

The present invention provides methods for manufacturing swellable packers that include molding the packer onto the tube. Multiple types of molding are contemplated, including injection molding and compression molding. Some of the steps of molding a swellable packer are shown in FIGS. 3A-D and FIGS. 4A-D, according to an embodiment of the present invention. FIG. 3A illustrates a tube 11 and end caps 14 that have been secured to the tube 11 such that the end caps 14 may be centered on the tube 11, possibly using shims and screws as described above. FIG. 4A shows a cross-sectional view of an end cap 14 around tube 11, illustrating that the inner diameter 142 of end cap 14 may be slightly larger than the outer diameter 111 of the tube 11.

The tube 11 and the end caps 14 secured to tube 11 may then be placed in a bottom cavity 33 located in the bottom of a mold 32, as illustrated in FIG. 3B and FIG. 4B. In this embodiment, the end caps 14 may rest on semi-circular supports 31 located at either end of the bottom of the mold 32. Corresponding semi-circular supports may also be located at either end of the top of the mold 34. The diameter 312 of the supports 31 may be the same as the outer diameter 141 of the end caps 14 so that the end caps 14 (and thus the tube 11) may be securely fixed in the mold when the top of the mold 34 is closed, as shown in FIG. 3C and FIG. 4C. Thus, the position of the outer diameter of the end caps 14 may determine the position of the outer surface of the packer 10 with respect to tube 11, creating a packer which may be round and have a straight axis despite the tube 11 about which the packer is molded being out-of-round or bent. Furthermore, supports may be used which have removable seats 311, allowing the seats to be replaced when worn.

Once the mold is closed, as in FIG. 3C and FIG. 4C, the packer can be molded by molding swellable polymer 13 in molten form within the mold cavity 33 and around the support tube 11. Swellable polymer 13 may be supplied to the mold by various techniques including injection molding and compression molding. In injection molding, molten polymer is injected into a mold which contains a tube 11 to form a packer 10. In compression molding, sheets of swellable polymer 13 may be laid in the top of a mold 34 and the bottom of a mold 32 and then the mold may be closed around a tube 11 to compress the sheets of polymer 13 to create a packer 10. Compression molding may more easily allow for layers of reinforcing fabric to be incorporated into the packer and/or for the creation of more complex packer shapes according to embodiments of the invention. For example, packers can be formed that are not circular cylinders as illustrated, but may be provided with steps along the length of the packer. Further, unique profiles can be created, such as a generally cylindrical packer having a crowned shape with a larger diameter at a middle portion than at the end portions.

Once the molding process is complete, the mold can be opened, as in FIG. 3D and FIG. 4D, and the molded packer 10 can be removed from the mold. During the molding process, some of the polymer may be forced into the gap between the end cap inner diameter 142 and the tube outer diameter 111, as shown in FIG. 5 (although exaggerated in scale for clarity). This may make a stronger bond between the swellable polymer 13, the tube 11, and the end cap 14. Any polymer that extends too far beyond the end cap may be trimmed after completion of the molding process.

Also shown by FIG. 5, a bonding agent 15 may be applied to the surfaces of the tube 11 and/or end cap 14 before the molding process to achieve a better bond with the swellable polymer. The bonding agent 15 may also be applied to all or a portion of the length of the tube 11 which corresponds to the length of the packer 10 before the swellable polymer 13 is molded unto the tube 11. One bonding agent that is effective is THIXON 532-A-EFAPH available from Dow Chemical.

Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

That which is claimed:
 1. A method of manufacturing a swellable polymer packer on a support tube, the method comprising the steps of: positioning one or more end caps on the support tube, the end caps defining a size and shape; positioning the end caps and support tube on one or more corresponding supports of an open mold cavity; closing the mold cavity; molding swellable polymer in molten form within the mold cavity and around the support tube; and opening the mold cavity.
 2. The method of claim 1, wherein a position of an outer surface of the packer relative to the support tube is determined by a position of the one or more end caps relative to the mold cavity.
 3. The method of claim 2, wherein the support tube is out-of-round or bent so as to define a central axis that is not straight.
 4. The method of claim 1, wherein the step of molding swellable polymer in molten form within the mold cavity and around the support tube comprises injecting molten polymer into the mold.
 5. The method of claim 1, further comprising: before closing the mold cavity, layering at least one sheet of a swellable polymer in the open mold cavity.
 6. The method of claim 1, wherein the step of molding swellable polymer in molten form within the mold cavity and around the support tube comprises compression molding.
 7. The method of claim 1, wherein the supports have replaceable seats.
 8. The method of claim 1, wherein the outer surfaces of the end caps are at least partially circular in cross section and the support surfaces of the supports are least partially circular in cross section, and wherein the support surfaces have the same diameter as the outer surfaces of the end caps.
 9. The method of claim 1, wherein a cross-sectional dimension of the swellable packer changes along the length of the packer.
 10. A swellable packer comprising: a support tube; one or more end caps secured to the support tube; and a swellable polymer molded around the tube such that a position of the outer surface of the swellable polymer relative to the tube is determined by a position of the end caps.
 11. The swellable packer of claim 10, wherein a cross-sectional dimension of the swellable polymer molded around the tube has a cross-section that changes along a length of the packer.
 12. The swellable packer of claim 10 wherein at least one end cap is secured to the support tube using set screws.
 13. The swellable packer of claim 10 wherein at least one end cap defines an inner surface that is at least partially circular and having a diameter that is larger than a nominal outer diameter of a support tube.
 14. The swellable packer of claim 13 wherein a portion of the swellable polymer is molded between the inner surface of the end cap and the outer diameter of the support tube.
 15. The swellable packer of claim 10 wherein the support tube is out-of-round or bent so as to define a central axis that is not straight. 